Chemistry - Rocks and Building Materials

We get almost every raw material from the Earth.

Blocks of stones are cut out from the ground, rocks such as limestone.

The disadvantages of quarrying is that they produce noise and dust pollution. Wild habitats can be destroyed and scenic views where limestone is most commonly found which damages tourism and upsets local people.

However, quarries provide us with useful materials, employment and brings in big money that help with the local economy.

The advantages and disadvantages need to be weighed before a quarry takes place. 

The positioning is also important because they need to ask how easily it can be dug out and are there good transport links. 

Of course, once the rock has been removed the soil and trees can be replaced. like some quarries that have turned into nature gardens and shops.

Limestone's chemical formula is CaCO3. 

If limestone is dropped into acid then it will fizz steadily. 

The acid and calcium carbonate will form a salt, carbon dioxide and water.

If hydrochloric acid (2HCl) was to react with limestone (CaCO3) then the products would be:

• Calcium chloride (CaCl2)
• Carbon dioxide (CO2)
• Water (H20).

Rainwater is always slightly acidic and can form cracks, and sometimes hollow limestone by dissolving it.

Pollution will make the rain more acidic, such as nitrogen oxides can be broken down into nitric acid which causes acid rain.

In polluted areas detail to statues have been lost and houses made out of limestone have crumpled down.

However, if powdered limestone is added to acidic lakes and rivers, it will neutralise them. The advantage of using limestone is that if added to much it will not make the lake alkaline and wil simply remain undissolved and settle out harmlessly.

Also, the calcium sulphate produced is harmless.

The equation would be:

calcium carbonate (CaCO3) + sulfuric acid (H2SO4) goes to

calcium sulfate (CaSO4) + water (H2O) + Carbon Dioxide (CO2)

If limestone if heated strongly then the compound is broken up.

The limestone will be broken into two products, calcium oxide and carbon dioxide.

The mass of the product will be lower than the mass of the reactant because weight is lost through the carbon dioxide because it escapes into the atmosphere.

This is called thermal decomposition. This is where one substance is broken up into two or more different substances.

Calcium hydroxide is a strong alkaline, if it touchs with your skin, it would react with the water and burn you. It also reacts with water to produce calcium hydroxide (Ca(OH)2).

If calcium hydroxide is dissolved in water it will become an aquasous liquid and this can be used to test for carbon dioxide. Because if this substance is reacted with carbon dioxide then the liquid will turn milky.

Limestone is heated to form calcium oxide.Cement is formed form this by adding products found in clay. If added to water, cement forms a paste that will turn back into a solid through some more chemical reactions.

Mortar can then be made by adding sand to cement which makes a paste with water that is used to bind bricks together.

To make concrete the cement is added with crushed rock or gravel. Concrete is first a thick liquid that can be moulded into any shape and after ten hours, with slowly chemical reactions becomes rock hard.

The aggregate use to make concrete can be found through the ash produced by power stations to help keep the costs down.

Making cement from limestone produces carbon dioxide. Concrete however reabsorbs some of the CO2 and it hardens.

Many people like concrete buildings however many find it unattractive.

Using concrete has many adavantages such as:

1. Cement is relatively cheap. 2. Powdered cement is easy to transport.   2. Aggregate is cheap and can be found everywhere. 3. Liquid concrete can be mixed on site. 4. Liquid concrete can be moulded into any shape. 5. Once set, concrete is rock hard.

However it is brittle so it will break easily if bent or stretched.Concrete is often reinforced with steel rods that stop it stretching or cracking.